1. Field of the Invention
The present invention relates to a flow cell device, sensor unit and assay apparatus. More particularly, the present invention relates to a flow cell device, sensor unit and assay apparatus in which non-specific adsorption can be prevented in a rapid assay.
2. Description of the Related Art
An assay apparatus for assay in utilizing attenuated total reflection is used for various kinds of studies in a biochemical field or the like, for example to study interaction of protein, DNA and various biomaterials, and to select candidate drugs by screening. Also, the technique is useful in the fields of the clinical medicine, food industries and the like.
A surface plasmon resonance (SPR) sensor is known as an assay apparatus in utilizing attenuated total reflection. Surface plasmon is a term to mean the compressional wave created on the surface of the metal and included in plasmon as quantized expression of the compressional wave. Free electrons in a metal vibrate to generate the compressional wave.
U.S. Pat. Nos. 5,164,589 and 5,313,264 (corresponding to JP-B 3294605) disclose the SPR assay apparatus with Kretschmann configuration. In the assay apparatus, the sensing surface is positioned opposite to an interface where a metal thin film is connected with a dielectric block. The sensing surface is caused to create surface plasmon resonance. Reaction of samples is assayed by detecting the SPR on the sensing surface. Then total reflection of the illuminating light occurs.
Upon the total reflection created on the metal/dielectric interface, a small component of the light passes through the metal film without reflection, and penetrates to the sensing surface. A wave of the penetrating component is called an evanescent wave. Surface plasmon resonance (SPR) is created when frequency of the evanescent wave coincides with that of the surface plasmon. In response to this, intensity of the reflected light attenuates remarkably. In the assay apparatus, the attenuation in the reflected light reflected by the metal/dielectric interface is detected, to recognize creation of the SPR on the sensing surface.
A sample or biomaterial, such as protein, is handled as sample fluid for the purpose of preventing deactivation or modification due to drying. The sample fluid contains biomaterial and fluid medium, examples of which include pure water, physiological saline water, liquid buffer and the like. U.S. Pat. Nos. 5,164,589 and 5,313,264 (corresponding to JP-B 3294605), for assay of reaction of a sample or biomaterial, suggest a use of a flow channel which is positioned on a sensing surface and where a sample fluid flows. A linker film is formed on the sensing surface for immobilizing ligand or sample. Ligand fluid is introduced in the flow channel, to immobilize the ligand on the linker film. After this, analyte fluid is introduced for causing the ligand to contact the analyte, to assay the interaction between the ligand and analyte.
A body of the assay apparatus has an assay stage. A sensor unit of a chip type includes a glass substrate and a thin film of metal formed thereon, and is placed on the assay stage for assay. Tubes or conduits are connected with pumps, valves and the like, to cause the sample fluid to flow from a reservoir directly to the flow channel. However, there is a problem in risk of contamination caused by mixing of residual sample in the conduits with the sample fluid.
A suggested SPR assay apparatus includes pipette devices each of which has a pipette tip and a pipette head. The pipette tip has a partially conical surface, and has an end opening. The pipette head is connected with and supports the pipette tip in a removable manner. The sample fluid or other liquids are introduced from a reservoir to the flow channel of the sensor unit. The pipette tip is detipped for renewal at each time of a change of the liquids, so a contamination of the liquids is prevented in introduction to the flow channel.
A sensor unit is used in the SPR assay apparatus. The sensor unit includes a flow cell device, a prism and a sealing structure. The flow cell device has a flow channel. The prism is overlaid with a thin film of metal. The sealing structure keeps a lower surface of the flow cell device secured to an upper surface of the prism or keeps the flow channel positioned on the thin film. A linker film is formed on the thin film of the sensor unit as described above. Pipette devices are used for introducing fluid into the flow channel for assay, the fluid being one of ligand fluid, analyte fluid and the like.
There are regions on the linker film, which are a measuring region having bindable groups for ligand, and a reference region after deactivation of the bindable groups. A light source is driven to apply light to the measuring region and the reference region. Reflected light from those are photoelectrically converted by a photo detector, to output a measuring signal and a reference signal. The signals are arithmetically processed to obtain a difference, ratio or the like and are analyzed. So a result of high precision can be obtained after canceling electrical noise due to individual specificity of the sensor unit and changes in the temperature of fluids. Influence of non-specific adsorption is suppressed by the analysis, the non-specific adsorption be in a problem of unwanted binding of sample on the linker film in a biochemical sample, such as protein, DNA and the like.
However, a difference is likely to occur in the amount of the non-specific adsorption between the measuring region with the bindable groups and the reference region without the bindable groups, due to the difference in the characteristic of the surface. The difference in the amount to the non-specific adsorption cannot be eliminated even after precise analysis.
To introduce ligand fluid to contact only the measuring region, two or more of the flow channel should be formed and used. This may be effective in suppressing a difference between amounts of the non-specific adsorption without deactivating the bindable groups of the measuring region. However, a structure with two or more of the flow channel will enlarge the size of the sensor unit. For improvement in the SPR assay of the sample, higher precision and higher efficiency in assay with a great number of the sample at one time are desired. However, rise in the throughput of the assay is desired, but is impossible due to an enlarge shape of the sensor unit.